Haha! No bother, answering questions gives me a break from writing SOPs
In the Reason Code Library, there's a Skip Adjustment Code setting that should be set to "Skip ERA Adjustment" for any reason code that you don't want to write off. For instance, we have CO-96 set to skip the ERA adjustment with a Transaction Detail Status of None so that it doesn't automatically move the balance to the next COB bucket.
If your client has Contracts set up for those payers, you'll want to check they haven't enabled the option to automatically adjust charges by mistake. It's on the General tab in the Contract Maintenance window. This one is probably less likely to happen but you never know.
If I think of any other place in NextGen there could be an auto-adjustment, I'll update the thread.